The present invention relates to a semiconductor laser equipped with means for reinjecting the spontaneous emission into the active layer and which is used in optical telecommunications.
The technical field of the invention is that of so-called double heterostructure semiconductor lasers. Such a structure is constituted by a stack of semiconductor layers deposited by epitaxy on a monocrystalline substrate. Starting from the substrate, there is generally an optional buffer layer, a first confinement layer, an active layer responsible for the light emission, a second confinement layer, a contact layer and finally a metal layer. The double hterostructure character results from the fact that the active layer is surrounded by two layers having a different composition from that of the active layer.
In the case of lasers emitting between 0.8 and 0.9 .mu.m, the confinement layers are of alloy Ga.sub.1-x Al.sub.x As and the active layer and substrate of GaAs. For lasers emitting between 1.3 and 1.65 .mu.m, the confinement layers are of Ga.sub.1-x In.sub.x As.sub.1-y P.sub.y and the active layer and substrate are of InP.
Using such structures, the threshold current density is approximately 1 kA/cm.sup.2. In order to reduce the actual threshold current, use is made of different methods making it possible to define an active ribbon or tape of limited width. The threshold current is then approximately 1 mA.
The object of the present invention is on the one hand to reduce the threshold current density for structures having large surfaces and on the other hand to reduce the threshold current for structures with a lateral limitation.